The present invention relates to a printing paper capable of forming a color image with excellent fixability, using an aqueous ink composition containing a water-soluble dye such as a water-soluble cationic dye and, in particular, to a printing paper suitable for ink jet recording. It also relates to a composition for forming a dye-receiving layer for such a printing paper, an ink composition suitable for the same, and a method for forming an image using them.
As one means for fixing an image information prepared by the use of a personal computer, etc. on a printing paper in the same manner as in silver salt photography, a method of forming a color image on a printing paper according to an ink jet recording system using an aqueous ink composition is considered hopeful.
In such an ink jet recording system, a liquid, aqueous ink composition containing a water-soluble dye, water, a polyalcohol, etc. is letted out and adhered onto a printing paper having a dye-receiving layer at the dye-receiving layer through nozzles, using a driving power such as electric field, heat and pressure to thereby form an image thereon.
The water-soluble dye to be employed in the aqueous ink composition for such an ink jet recording system is essentially a water-soluble direct dye or acidic dye (hereinafter referred to as "anionic dye") having a sufficient fixability to cellulose constituting paper which is essentially used as a recording medium and capable of yielding a black color by itself. Accordingly, in general, a basic dye (hereinafter referred to as "cationic dye") is not used as the dye in an aqueous ink composition at present because of its drawbacks that its fixability to cellulose is not sufficient as compared with anionic dyes and that it cannot form a black color if not mixed with others.
On the other hand, the ink-receiving surface of the printing paper to be used in the ink jet recording system using such an aqueous ink composition has a dye-receiving layer composed of various additives dispersed in a water-soluble high polymer having a high affinity for dyes so as to prevent the aqueous ink composition applied thereto from bleeding.
Conventional water-soluble anionic dyes used in the ink jet recording system are, after having been transferred to the dye-receiving layer, captured in the dye-receiving layer due to the interactions such as van der Waals force and hydrogen bonding between them and the constituent components in the dye-receiving layer, according to the theory of dyeing. Therefore, after formation of images, when other substances such as solvents or resins having a higher affinity for these dyes are brought into contact with the formed images or when some heat energy enough to cancel these interactions is applied thereto, then the dyes will dissolve out or transfer from the dye-receiving layer to such other substances whereby the thus-formed images will be blurred without having complete fixation to the layer unlike so-called silver salt photographs. Being different from silver salt photographs, therefore, therefore, the images formed by the ink jet recording system are problematic in this respect.
As some means for solving the problem, it has been proposed to chemically fix such dyes to a dye-receiving layer by forming chemical bonds between the dyes and the compounds constituting the dye-receiving layer (see JP-B 62-798, 63-11158, U.S. Pat. No. 4,694,302, JP-A 1-225585, etc.--the terms "JP-A" and "JP-B" as referred to herein mean an "examined Japanese patent publication" and an "unexamined Japanese patent application", respectively). Concretely, it has been proposed to use reactive dyes as the dye component in the ink composition so as to form covalent bonds between the reactive groups in the reactive dyes and the active groups in the dye-receiving layer or to form ionic bonds between anionic dyes and cationic organic polymers or cationic inorganic low-molecular compounds in the dye-receiving layer.
However, the conventional means of chemically fixing dyes in the dye-receiving layer by forming chemical bonds therebetween still were problematic in that the degrees of reactivity of the dyes and the dye-receiving layer were too high to attain sufficient preservation of inks and printing papers themselves and also images formed and to realize the fixation of the formed images comparable to that of silver salt photographic images and that, on the contrary, their reactivity was not sufficient so that the reaction between them could not be finished in a short period of time and therefore a long period of time was needed for forming stable images. In addition, the conventional means had other problems that they often needed some auxiliary devices for heating, etc. so as to fix the images, the preparation of dyes for the means was often difficult and the usable color hue range was limited. As further problems in these conventional means, the solvent resistance and the light fastness of the color images formed on printing papers by these means were still unsatisfactory so that the fixation of the images thereon was insufficient even though waterproofness was imparted to the images.
Therefore, in order to make the images formed by the conventional ink jet recording system usable even in the field that needs high image durability, for example, including photographs for identity cards and prints for outdoor exhibition, the improvement in the fixation of the color images formed is strongly desired along with the improvement in their saturation and resolution so as to be able to obtain high-quality color images.
Heretofore, particular ink jet recording papers having a dye-receiving layer formed thereon have been needed as printing papers for ink jet recording. However, it is strongly desired that any unlimited base materials having no dye-receiving layer thereon, such as household or officehold high-quality papers, art papers and OHP sheets, may be applied to ink jet recording.